A microstrip antenna includes a first metal layer that constitutes an antenna element, a second metal layer that constitutes a ground, and a flexible member that separates the first metal layer and the second metal layer by a predetermined distance. The first metal layer and the second metal layer each are made of a metal or a metal foil. At least one of the first metal layer and the second metal layer is not adhered to the flexible member but is in close contact with the flexible member by a close contact unit. The close contact unit is a clamping mechanism including a first plate, a second plate, and a connecting member. The first plate and the second plate are connected to each other by the connecting member. The connecting member is an elastic body.